Abstract: A control system for a nuclear steam power plant having a reactor, one or more once through steam generators and a turbine includes a reactor control subsystem responsive to a power demand input to cause the reactor to deliver thermal power commensurate with the power demand input to the once through steam generator, one or more feedwater control subsystems sensing the thermal power delivered by the reactor to control feedwater flow to the once through steam generator, such as via a regulating valve and/or a feed pump, to match the thermal power delivered by the once through steam generator to the turbine with the thermal power delivered by the reactor, and a turbine steam demand control subsystem responsive to the thermal power delivered by the once through steam generator by sensing steam pressure to control a governor valve to admit steam to the turbine to cause the turbine operation to match the steam supplied by the once through steam generator such that the nuclear steam power plant is plant process con